Batteries which are provided for use in hybrid vehicles or electric vehicles are referred to as traction batteries since they are used for feeding electrical drives. In order to obtain the power data and energy data which are required in hybrid vehicles or electric vehicles, individual battery cells are connected in series and partially additionally in parallel. In the case of electric vehicles, for example 100 cells or more are connected in series, with the result that the total voltage of the battery can be up to 340 V. Batteries which are used in hybrid vehicles also usually exceed the voltage limit of 60 V which is categorized as unproblematic in the case of touching by humans.
FIG. 1 illustrates the basic circuit diagram of a battery system according to the prior art. Such a battery system is described, for example, in DE-A 10 2010 027 850 with a detailed block circuit diagram.
In particular, FIG. 1 shows a battery 10 with assigned integrated electronics. A multiplicity of battery cells 11 are connected in series in order to obtain a high output voltage which is desired for a respective application. Optionally, the battery cells can also be connected in parallel in order to obtain a high battery capacity.
A charging and isolating device 14 is connected between the positive pole of the series circuit of the battery cells 11 and a positive battery terminal 12. In addition, an isolating device 15 is located between the negative pole of the series circuit of the battery cells 11 and a negative battery terminal 13. The charging and isolating device 14 and the isolating device 15 each comprises a contactor 16 and 17 as isolator switches. These contactors are provided for disconnecting the battery cells 11 from the battery terminals 12, 13, in order thereby to connect the battery terminals 12, 13 in a voltage-free fashion when required. Other switching means which are suitable for this application can also be used instead of contactors.
In addition, a charging contactor 18 is present in the charging and isolating device 14. A charging resistor 19 is connected in series with the charging contactor 18. The charging resistor 19 limits a charging current for the buffer capacitor which is connected into the DC voltage intermediate circuit of a customary battery-fed drive system when the battery is connected to the DC voltage intermediate circuit. When predefinable events occur, the battery can be activated or deactivated at one pole or two poles with the arrangement of the charging and isolating device (illustrated in FIG. 1) in the positive line and the isolating device in the negative line. For this purpose a control device which is not illustrated provides corresponding signals which activate the contactors.
By using the charging resistor 19, balancing currents can also be limited during the activation of the battery. In the case of an activation process, the charge switch 18 is firstly closed here in the charging and isolating device 14, with the isolator switch 16 opened, and additionally, if desired, the isolator switch 17 in the isolating device at the negative pole of the battery system is closed. The input capacities of externally connected systems are then charged by means of the charging resistor 19. If the voltage between the positive pole and the negative pole of the battery system differs only insignificantly from the total voltage of the battery cells, the charging process is terminated by closing the isolator switch in the charging and isolating device 14. The battery system is then connected with low impedance to the external systems and can be operated with its specified power data. Overall, the balancing currents which occur between the external systems and the battery system when the battery system is activated, can be limited to permissible values.
FIG. 2 illustrates an electric drive system, known, for example, from DE-A 10 2010 027 864.5, for an electric vehicle or hybrid vehicle as a basic circuit diagram. Here, a battery 20 is connected to a DC voltage intermediate circuit which is buffered by a capacitor 21. A pulse-controlled inverter 22, which makes available sinusoidal voltages, which are phase-offset with respect to one another at three outputs via, in each case, two switchable semiconductor valves 22a, 22b and two diodes 22c and 22d, for operating an electric drive motor 23, for example a three phase machine, is connected to the DC voltage intermediate circuit. The capacity of the capacitor 21 has to be large enough to stabilize the voltage in the DC voltage intermediate circuit for a period of time in which one of the switchable semiconductor valves is activated.
The electric drive system which is known from DE-A 10 2010 027 864.5 comprises a battery 20 which has, similarly to the battery 10 illustrated in FIG. 1, a multiplicity of battery cells which are connected in series. A charging and isolating device is present in the positive line and an isolating device is present in the negative line, between this series circuit comprising battery cells and the positive and negative terminals of the battery 20. By means of these isolating devices it is possible, as in the case of the battery 10 from FIG. 1, to disconnect the positive pole of the battery and/or the negative pole of the battery from the battery cells in the case of an accident or in the event of a malfunction when a connectable of the charger device is not operating satisfactorily, and thereby switch to a voltageless state. In particular, two-pole disconnection of the battery from the traction on-board power system is proposed in order to place the battery in a safe state. The electric charge which is stored in the battery cells is still retained in this case.